1. Field of the Invention
This invention relates generally to navigation systems, and more particularly to systems for determining the closest navigation point such as an airport or a very high frequency omni-range (VOR) navigational ground station to the aircraft.
2. Description Of The Prior Art
It is desirable to be able to determine the position relative to the aircraft of the closest navigation point such as a VOR or airport so that the appropriate VOR may be tuned in and the closest airport be known in the event of an emergency. The determination of the closest navigation point may be done either manually through the use of navigation charts or automatically by feeding the position of the aircraft into a computer that has stored therein location and other information for each navigation point. While these systems do provide a way to find the closest navigation point, the use of navigation charts requires that large and cumbersome charts covering the area over which the aircraft is flying be carried and requires an experienced navigator to make judgments as to the closest navigation point. In present computer based systems, data defining each navigation point in the world, for example, approximately 3600 VORs and 6000 airports is stored in a memory. The stored information for each navigation point includes a location identifier (such as an airport identifying word), latitude and longitude coordinates for the navigation point, the frequency of the transmissions from the navigation point, elevation and other related data. Typically the file is ordered alphabetically by the location identifier word, and in order to determine the closest navigation point to the present position, the coordinates of each of the 3600 VORs and 6000 airports are compared with the present position of the aircraft. Because of the number of comparisons that must be made, such a system does not make optimum use of computing capacity and computing time. The invention eliminates such a comparison requirement, and substitutes a look-up table approach.